Roadway lighting is a fundamental public service that leads to a safer environment for both pedestrians and drivers. It is estimated that lighting alone accounts for around 3% of the total U.S. electricity consumption. Currently, street lighting applications mostly involve high-intensity discharge (HID) sources such as metal halide lamps and high-pressure sodium (HPS) lamps. As the energy crisis spreads across the world, energy conservation is becoming an urgent priority. Light-emitting diodes (LEDs) are fourth-generation light sources that have recently appeared as an energy-efficient solution to street lighting. (LEDs are currently used and are gaining credibility in street lighting applications but are only beginning to become viable for roadway lighting applications.) This report presents a comprehensive literature review that covers the current state of technology in LED roadway lighting, detailed comparison of LED roadway luminaires with HID roadway luminaires, test procedures for photometric measurements of roadway lighting installations, and IDOT roadway lighting requirements. LED luminaires provide the advantages of energy efficiency, longer lifetime, good color characteristics, improved mesopic vision conditions, lack of warm-up time, compact size, directional light, reduced light pollution, environment-friendly characteristics, dimming capabilities, breakage and vibration resistance, and more uniform light distribution. The Department of Energy (DOE) GATEWAY demonstration projects provide good information on the potential benefits of the replacement of HPS streetlights with LED streetlights. However, LEDs are currently not frequently utilized in street lighting applications due to their lower luminous efficacy, higher heat conversion rate, higher installation cost, and issues in obtaining white light. Trade-offs between color correlated temperature and lumen output, and between color shift of LED light sources over time, lumen maintenance (LED life expectancy), and thermal management are the critical issues of LEDs that should be properly addressed in street lighting applications. Because of the significant differences in HID and LED technology, there has been a gap in industry test standards and test procedures for product comparisons and ratings. Thus, ENERGY STAR® criteria, along with other important new standards and test procedures, have been released and continue to be developed. Some institutions also published their own specifications for LED roadway lighting. There is a significant push by the industry to research and develop LED luminaires for street lighting, and this is evidenced in the number and improved characteristics of new products being released by practically every major player in the street lighting sector. Given the clear trend toward the use of LED luminaires in the industry, it is expected that efficient LED luminaires for highway applications will be available in the near future for higher mounting heights and lumen output requirements. (Author/publisher)
Samenvatting